Large complicated structural parts made from light alloys, composites, polymers, plastics and other materials can be used for automotive bodies, airplane skin and frames, missiles, space vehicles, ships and architecture. Presently, most panels and large thin parts from light alloys are fabricated by high speed or chemical milling of thick plate billets. This processing is expensive, material wasting, time and labor consuming. Another problem presents providing high, uniform and isotropic properties in final products. Usually, thick plates are produced by rolling of large ingots with many metallurgical defects and insufficient rolling reductions to heal these defects. Therefore, many high strength aluminum alloys show properties anisotropy, low ductility and brittleness in a short transverse direction. Also, a large volume of the removed material during milling operations results in product distortion requiring additional straightening operations.
Much more effective forming of panels in forging dies requires high pressures. For aluminum alloys, the average pressure is about 10,000 tons per a square meter. Practically, it may be applied to relative small panels as very powerful presses for large panels are not available. Among other approaches known in the art for fabrication of large panels are the die-rolling process (see U.S. Pat. No. 3,415,095), the step-forging process (see U.S. Pat. Nos. 3,521,472; 3,847,004; 4,608,848; 4,770,020 and 4,907,436) and the progressive forging process (see U.S. Pat. No. 5,327,767). All these techniques were found unpractical because of high cost, poor filing of sculptured dies, complicated tool, and/or possibility for generation of defects.
The advanced concept of the forging-rolling process was introduced in U.S. Pat. No. 5,673,581. In this case, by selecting sufficiently large ratios of a contact length between billet and die to a billet thickness, contact friction prevents material flow into directions of billet length and width and provides material flow into sculptured dies. Therefore, complicated and large panels can be fabricated. However, a few technical shortcomings still remain. First, during processing, forming dies slide along guide surfaces under high pressure with large friction and intensive wear. Second, two sets of top and bottom dies including difficult to fabricate ring dies of large curvature are needed. Third, a circular working zone between dies does not provide the optimal forging conditions with the increased contact length and an excessive load. Fourth, the tool and apparatus are complex, expensive and difficult for realization at standard presses. Fifth, forming of panels with thin boards, deep stiffeners and small transition radii may lead to such defects as laps, holes, and blinks.